This invention relates to a process for determining the shifting time for a transmission ratio change in an infinitely variable transmission which simulates the operation of a stepped transmission.
German Patent Document DE 41 20 540 C1, discloses an arrangement for controlling an infinitely variable transmission in such a manner that a stepped transmission is simulated which can be influenced directly by the driver. For this purpose, a control unit adjusts the pressure conditions on the infinitely variable transmission such that a desired transmission ratio ue.sub.des determined in the control unit as a function of the driver's shifting desire, is adjusted at the transmission. A change of the desired transmission ratio demanded in this manner cannot take place abruptly. Rather, it is carried out during a preset shifting time, taking into account the loading of the transmission, in order to generate a shifting comfort which is convenient for the driver.
As a rule, automatically shifted stepped transmissions used in passenger cars are constructed of gear wheels arranged to form planetary gear trains. By means of such gear trains preset transmission ratios can be shifted by clutches and brakes acted upon by pressure. In such transmissions, it is also important that the change of the transmission ratio (that is the pressure reduction in the case of the clutches and brakes operated at the old transmission ratio, on the one hand, and the pressure buildup in the case of the clutches and brakes operated in the future gear, on the other hand) not take place abruptly; rather, for both technical and comfort related reasons, it must be carried out during a preset shifting time.
One objection of the present invention is to provide a method and apparatus for determining such a shifting time in such a manner that the shifting comfort is adapted to a driver's feeling of comfort.
This object is achieved according to the invention by taking into account all variables which have a significant influence on a change of the transmission ratio. In particular, the position of the shifting (starting transmission ratio and target transmission ratio; for example, shifting from the 4th transmission ratio to the 5th transmission ratio) as well as the direction of the shifting (shifting from the 4th transmission ratio to the 5th transmission ratio as opposed to the shifting from the 5th transmission ratio to the 4th transmission ratio) have a significant influence on the shifting comfort. This influence is taken into account in that a basic shifting time is determined separately for every shifting and for every shifting direction.
According to the invention, a rotational speed factor is determined, which takes into account the change of the rotational input speed of the transmission caused by the change of the transmission ratio. Since this rotational speed change acts upon the rotating masses on the input side of the transmission as well as of a driving engine connected in front of the transmission, that portion of the influence on the shifting comfort which results from the change of the rotational energy of these masses is taken into account. With an increase of the rotational input speed, the rotational speed factor, and thus also the shifting time, will increase.
In addition, a load factor is determined, which takes into account the load applied to the transmission input. In the case of low loads, a soft, less noticeable shifting operation is desirable, which must meet high requirements for shifting comfort. In contrast, in the case of a high load, the desire to accelerate is a primary concern, which can also be met by utilizing the rotational energy. In the latter case the desire for comfort will not be as important, so that hard shiftinq is also acceptable. For this reason, when the load decreases, the load factor (and thus the shifting time) will increase. According to the layout, it is possible that, in the case of very high loads, the load factor reaches negative values in order to counteract the rotational speed factor for utilizing the rotational energy.
The application of the process can be achieved in a particularly simple and cost effective manner in the form of a programmable control, using a digital data processor.
According to a further embodiment of the invention, the basic shifting time is determined also as a function of the driving condition (drive or coasting). As a result, it is taken into account that the shifting comfort for a driver is influenced not only by the amount and the course of a shifting jolt, but also by its direction. This further development recognizes that a shifting jolt during coasting is felt to be more bothersome than a shifting jolt in drive. (This is caused by the fact that the driver is better supported by his seat in the drive operation than in the coasting operation.) On the other hand, during an acceleration a shifting jolt is accepted as necessary for the acceleration, or even as a sign of a sporty driving style, whereas, in the case of a deceleration during coasting, shifting jolts cause the impression of an interruption of the deceleration and are therefore felt to be bothersome.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.